1. Technical Field
This disclosure relates generally to a gear pump apparatus, such as a trochoid pump, which is designed to use the meshing of gears to pump fluid by displacement and may be employed with automotive brake systems.
2. Background Art
Japanese Patent First Publication No. 2014-25352 discloses the above type of gear pump apparatus which includes, as illustrated in FIG. 18, a gear pump 19 equipped with an outer rotor 19a, an inner rotor 19b, and a sealing mechanism 111. The sealing mechanism 111 works to hermetically seal between a high-pressure region and a low-pressure region near one of ends of the gear pump 19.
The sealing mechanism 111 includes a hollow frame-shaped inner member 112, an annular rubber member 113, and a hollow frame-shaped outer member 114. The annular rubber member 113 is disposed between an outside peripheral wall of the inner member 112 and an inside peripheral wall of the outer member 114. The inner member 112 is fit in the outer member 114.
The outer member 114 is made of a plate which has a recess 114b and a protrusion 114c formed in and on one of end surfaces which faces the gear pump 19. The protrusion 114c is in contact with the end surface of the gear pump 19.
The parts of the sealing mechanism 111 are urged or biased by the discharge pressure of the gear pump 19 in a given direction. Specifically, the inner member 112 is disposed in abutment with a bottom surface of a recess formed in a housing (not shown), while the protrusion 114c of the outer member 114 is placed in contact abutment with the end surface of the gear pump 19. This creates a hermetical seal.
The exertion of the discharge pressure on the outside peripheral surface of the outer member 114 results in deformation of the outer member 114, which will develop mechanical pressure F′ to grip the inner member 112 (which will also be referred to a gripping force below). If a coefficient of friction between the outer member 114 and the inner member 112 is expressed as a friction coefficient μ′, frictional force F4 created between the inner member 112 and the outer member 114 in FIG. 18 will be F4=μ′·F′.
The outer member 114 is, as illustrated in FIG. 18, urged by the pressing force F1 against the gear pump 19. More specifically, the discharge pressure is exerted on an entire area of one of the end surfaces of the outer member 114 (i.e., the left end surface of the outer member 114, as viewed in FIG. 18) which is father away from the gear pump 19, so that the outer member 114 is uniformly pressed against the gear pump 19 as a whole.
The outer member 114 is also biased by the frictional force F4 away from the gear pump 19 (i.e., in a direction opposite the pressing force F1). The frictional force F4 is exerted on an inner periphery of the outer member 114.
The outer member 114 is, as described above, pressed uniformly to the gear pump 19. Simultaneously, the frictional force F4 acts on the inner periphery of the outer member 114 in the direction opposite the pressing force F1, thus causing the outer member 114 to be deformed to have an outer peripheral portion thereof closer to the gear pump 19 than an inner peripheral portion is.
More specifically, the outer member 114 is deformed or rotated about a contact between an outer peripheral edge of the protrusion 114c of the outer member 114 and the outer rotor 19a, so that the inner peripheral portion is moved away from the gear pump 19, while the outer peripheral portion is moved closer to the gear pump 19. This results in an increased pressure acting on the contact between the outer peripheral edge of the protrusion 114c of the outer member 114 and the outer rotor 19a, thus increasing the resistance to sliding motion of the outer rotor 19a which will require an increase in torque for driving the outer rotor 19a and the inner rotor 19b. 